If you are on HRT you only need to use it when estrogen is about to spike.
I found that on HRT i could just take 12.5mg of aromasin the day after my injection, it worked out perfectly and has done for years.
Failing that if you are seriously gyno prone you could always try 20mg of nolva for a few days from the day of your HRT injection and for a few days after wards.

What exactly is the tired effect? is it physical or mental? Tired in the morning? or at a certain point in the day?

Unfortunately if you have 25mg pills there is absolutely no way to precisely get a lower dose especially 6mg. You can try to break up the pill but you never know if the drug is evenly distributed throughout the tablet. I hear you on aromasin making you tired. It practically disabled me with lethargy. I posted my experience in the forums.

If it were me, I would do one of two things:

1. If you want to stick with it at a lower dose get the liquid aro from a reputable source. Super easy to adjust dosage.

Or

2. Switch to Adex. That's what I did and I feel so much better.

Hope that helps