This is how I believe it works...The test you have left in your system at the end of the week will combine with the test from your next injection and so on. It will build up until you reach your true baseline for that dose which I believe takes around 5-6 weeks of injections to establish.
In theory, if you inject 100mgs once a week or 50mgs twice a week, it shouldn't matter. The reason is that if you believe esters cleave off as advertised, then you're going to get the same release regardless. If you inject 100mgs on Monday, you should have 35 mgs left on day 12. On day three, you would have about 3mgs active with 6mgs already consumed.
If you inject 50mgs, then you would have 6mgs left on day 12, with 1.5mgs active on day three. But when you inject another 50mgs, you will add another 1.5mgs, for a total of 3mgs. The first couple of days you'd have half of what you would had you injected 100mgs, but as you start to overlap, that will be a wash. But at day 7, before your injection, you should have the same level of mgs.
But I don't believe esters work that precisely. I believe that you get a surge the first day and the release tapers down dramatically. So the first day will yield your highest concentration. So I agree that spacing out the injections is preferable to help stabilize levels, although that runs contrary to the theory behind esters. And don't forget that 100mgs of test-c is actually only 69mgs of test.