Having read Rollo Tomassi's article here, my wife is strongly in the "The best case: She initiates during her fertile period if you don’t. She gets cravings for your D." category, but this seems to be the only time she is really into it (i.e. she is not opposed to having sex the rest of the month, but it's a bit star-fishy and often she does not climax, although she seems to enjoy the intimacy). For this reason, I'm hardly initiating at all (since she will when she really wants it).

My "dilemma" is that I will not get a hard no from her (some obvious circumstances excluded where she is really tired or sick) because she is very accommodating in general and I would feel a bit abusive exploiting this fact.

TL;DR is there a common strategy for dealing with a wife who enjoys sex during the fertile part of the cycle, but is indifferent (but not outright negative) otherwise?