Hi racjan- I think you're right about relying more on the level rather than the dose.
I've been using Estradot 100mcg plus two pumps of Oestrogel a day for the last month, having added the gel in as I was feeling so rubbish with just the patch- (my GP knew).
My blood test last week showed an oestrogen level of 193!
It is a worry 'overdosing' but having my blood checked did give me some reassurance and I am now waiting to see a Specialist.
In the meantime I have abandoned the gel (having had absorption issues with it in the past) and in desperation, I have bunged a second patch on.
If this doesn't work then my only other untried method is to use the implants which I'm really not keen on.