There is no way for us to know, but I would advise against using any dope that you have to press extra hard on the plunger to get the shot out. That's like the people that will heat their shot of dope or pills and shoot it quick since the stuff with become to thick to shoot otherwise. What do they expect will happen to it once it gets into their system? It's obviously going to thicken back up in them, which can cause a number of complications.
The issue seems to be that the cut has a low solubility in water. Lets say that you have 90mg of something in a 1ml syringe that is only soluble at 30mg/ml. Well you will only be able to dissolve less than 30mg with the first rinse, then another 30mg with each following rinse. Since some of the water in the first rinse will go towards dissolving the heroin, that leaves less to dissolve the cut. So when you get to the next shot after you already got most or all of the dope out of the first one, more of the water is going towards dissolving the cut than it did the first time. So if the heroin is soluble at 500mg/ml and a cut at 30mg/ml, that 1mg of water can't dissolve both the 500mg of heroin and the 30mg of cut, so some is going to be left over, although I don't know what percentage of either one will be left for the second rinse. The numbers I used are random (although I think heroins solubility in water is about the same as I listed) and were just used as an example to get my point across.
Since heroin is very soluble in water I don't think that these extra rinses are getting you more heroin. Just make sure to use enough water in the first rinse to account for the solubility, plus a bit more since the cut may be using up a bit of the water needed to dissolve the amount of heroin.
