I would have to say that your theory that blood doesn't reach muscles is false. After a while of googleing I found this article.
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1663362&blobtype=pdf
It says that in fact intramuscular injects are faster, although this varies with insulin type. I can
Hello! I'm not a medical professional, just the parent of a kid with diabetes. Insulin is injected subcutaneously because it needs to get into the bloodstream to be effective. Injecting into muscle tissue would actually reduce the effectiveness of the insulin.
Likely what you're seeing is the delay between the time you inject insulin and the time it starts working, typically about 15-20 minutes. The graph of the effectiveness starts low, rises fairly quickly after that 15-20 minutes to that 2 hour peak, then then gradually tails off. You may want to check on the 6 hour duration, many insulin experts will recommend you use 4 hours as the length of the insulin duration. So your blood sugar rises because of the immediate release into your system of the carbs in the ice cream, flooding your bloodstream with carbs, and the insulin takes a bit to get working.
Two possible options for you are to inject your insulin a little earlier, so it's in your system and working when you eat the ice cream, or to try to find ice cream with lower carbs. There are plenty of delicious options available. Either one of those will work better than injecting into muscle tissue. Good luck!