But if I'm allowed to say a little more, I'll just add that between any two points you can draw a straight line, so although it looks like the antibody level decreases linearly you would need more points to be certain of that. The values given by the test aren't necessarily steady points, the actual antibody level may fluctuate over the course of the day or the week so I don't think you can be certain how the antibody levels will drop.
But besides that, it's possible that antibodies decrease a lot, and you still have immunity due to B cells' ability to replace the antibodies rapidly and due to T cells. On the other hand, it's possible to have high antibody levels and still get reinfected because the Delta variant is different or stronger than the one that infected you the first time.
So measuring antibody levels may not help in answering your question, and you may just want to go with the numbers that were given elsewhere... What was it? That immunity seems to last at least 7 months? And wait that amount of time before getting the vaccine. Also, you might want to consider when you think you're most likely to be in close contact with people who might be infectious, such as in shul RH, YK, and aim for getting it before that.
Truth is, I don't know what advice I'd give myself if I were in that situation, so certainly am not in a position to advise others.