Hi waltzingfrog

from me too.
There is wide variation between individuals in the amount of absorption of estradiol from patches, but you should experience a more consistent dose once you've worked out how to get them to stick consistently. Also blood tests don't tell you that much because your levels will vary with time of day and depending when you changed the patch. Your doc should be going by your symptoms - and first checking that you are applying the product correctly.
Estradot are brilliant patches as they are so small and stick well - I've used them for years and have never had a reccuerrence of symptoms except when l've tried to reduce the dose. I do get into the habit of having a quick feel when in the loo, to make sure it is still stuck well down!
You mention hypothyroid - there is an interaction between estrogen metabolism and thyroid medication which I understand is more pronounced when using tablet HRT - but I can't find up to date detailed info on this.
I also take Utrogestan ( vaginally) but only on a cyclical basis.
Not sure what you mean by a synergistic effect in this context? From what I've read progesterone receptors can be activated by oestrogen in certain tissues (eg uterus), but also that added progesterone can also interfere with the beneficial effects of oestrogen. I'm a bit hazy on all of this!
I'm not clear what you were taking before - from what I can see you are post-menopausal but were given Femoston 1/10 which is a cyclical HRT designed to give a monthly withdrawal bleed. Then you went onto oestrogen only patches (and increased the dose) without added progestogen for a while - maybe 8 week or so? Then you started dydrogesterone (on a conti basis?) and then changed to utrogestan.
The thing is you will have built up your womb lining from the oestrogen - yes you will have been absorbing it, and adding the progesterone is now causing a bleed - the fact that you are bleeding when on a conti regime indicates that the lining was already thick and ready to come away - since usually withdrawal bleeding occurs after stopping the progesterone, and as you say, continuous progesterone is meant to prevent a bleed.
What dose of Utrogestan are you taking? If you do get bleeding on conti HRT then in the absence of nay other problems it usually means the progestogen dose needs to be increased - but in your case especially you probably still have lining to shed!
I wouldn't bother with a saliva test because these are very inaccurate and bear no relation to actual estradiol levels - they are only usfeul eg if women want to find out if they are still having a cycle and producing progesterone because the cyclical variation is apparent from the tests even though it doesn't reflect absolute hormone levels - if you see what I mean?
I'm wondering if you are outside UK as you mention saliva tests and dydrogesterone - which isn't available here?
Anyway I do hope this regime works for you - as I said it's the one I've been on for a few years - except I take utrogestan every 6-8 weeks because don't want to take prog the whole time! The most important thing is that you eventually feel well, and at the same time protect your womb.
Hurdity x