omsairam, I know exactly what you mean. When they happen at the same time it is better in terms of fertility. But it is very hard to know if they will be on the exact same day, or one or two days apart. Because the moon sign changes genders every 2.5 days, it is easy to O in the wrong moon. To 'guarantee' the gender, Odan recommend you mark off CD 9-18 on your chart. If your lunar O falls outside these days, then they say you will have the predicted gender if you get pg.
You can still TTC with your menstrual O on a month when your lunar calendar shows girl. The main thing you need to do is check that you will O in a boy moon and not just before it changes to a girl moon, as it can take some hours for conception to occur. I do OPKs, and for me I seem to O around 30 hours after I get a +ve. So as soon as I would get a +OPK, I would check what moon will be happening 30+hours later, and decide if it is a good month to TTC.
I am planning to give my lunar calendar a chance, but if I don't get pg using that, then I will definitely be TTC when my menstrual O happens in a girl moon as well.
I am good by the way! But my DS2 turns 4 very soon, so busy getting ready for that!