Alan
I feel there is nothing wrong with taking something from the market rather than all of it. You have to be very good to repeatedly take all or the vast majority of a gain when on offer by staying with the trend.
What should concern you more is that your set-up works more times than it fails. You are already ahead of the game because your only worry is what you are missing out on. Why worry if you know the next time you trade you are more likely to get something for your trouble.
You have already given yourself an extra chance by taking half profit and letting the other half run. If you want to try and expand on this further then you could divide again and operate from a 3 target perspective. Continue to do what you are already doing. But when you close your second let the 3rd run on.
If this fails to help then there is only one other method that I can think of. That is to make sure you know the instruments you trade well. Get a feel for how far the price may move before it tends to pull back and so on. Then when you feel you have a reasonable to good idea then apply realistic targets. How many I do not know but each time you dilute your deal size you will be reducing your overall profit when compared to trading from one perspective, unless you keep each mount equal.
However this issue is not about skill but dealing with one of your emotions so using pre-determined targets will help this matter. When a target or a specific set-up that you have established is your reason for deciding to close, then close one amount of your deal. Leaving the rest to continue until the market provides you with another target or set-up where you close another and so on until you are convinced this particular trend has come to an end.
This deals with emotions because once you take the profit you have it. The decision to close is taken from you and it becomes an automatic process without thoughts elsewhere. By allowing other amounts to continue then you are spreading your dealing allowing you to give those final parts just that bit more of scope to reach not all but further along the trend for you to take profit.
As an example consider a daytrader who cannot get out of the habit of getting 10 points profit and then the trader worries that by not closing there maybe nothing or less to show for it later.
The trader decides to take the 10 points but the price goes on to give 50. If on the other hand the trader had divided his capital to allow for 4 target levels. The trader decides to set targets at levels where the price appears to reach more regularly when trending. The decision is made to set targets at multiples of 10.
TOn the next deal this method is applied and 4 targets of 10, 20, 30, and 40 are obtained. Yet the price goes on another 10 points before the trend ends. In the meantime the trader has been able to run with the trend for longer than usual and has amassed a total of 10 + 20 + 30 + 40 = 100 points.
The trader still did not reach the end of the trend but was able to distance the emotions allowing for the trades to remain longer. I accept this may produce more costs and will not be seen as the most practicable way to trade but targets can be a way of dealing with this emotion. Of course the main issue with setting targets is that you can become blinded by them. When the price does not reach the next target you can fail to react to the market changes. Each target can be taken as soon as it is reached or if not a target then a specific price signal that you have chosen to close. If the remaining amount left cannot reach the next level then when it is clear a trend change signal has appeared you close all the rest still in a profit.
Its your mindset that you have to deal with. Last night I had a quick look on the DOW around 7.30pm and sold. I do not trade this very often so I am in unfamiliar ground. I got 15 points profit only for the move to continue and could have given me 65 points. Did I loose any sleep over it. NO, tomorrow or whenever is another day or deal. The important thing for me was to make profit and to learn from this experience but even if next time the same thing happened it would not bother me.
I stopped worrying about the 'what if I had done this or that' syndrome a long time ago. I have found that I do much better in terms of regular profits by the attitude of taking small profits. Because there are times when only a small profit is on offer and to linger hoping for a big trend to come along cost me in my earlier days. You must just apply your set-up and to block out these other thoughts.
Maybe you will never be able to judge a good trend and stay with it to the end, that does not make you any less a trader for it. Remember we all trade differently but the common denominator is making profit, try not to forget that.
Good luck