Hi Mis71Mum
If you are feeling OK on the combi/conti part of the HRT then sounds like you are OK with this progestogen. You will expect to feel normal pmt when you change back to the oestrogen only patches as this is what happens during a normal period before the bleed. After a few days you should feel good again

If your period is light it won't reflect your oestrogen levels particularly - just that your womb lining hasn't built up - because the progestogen is doing its job keeping it thin while you are taking it, and/or the oestrogen level is low. Also absolute oestrogen levels are not necessarily indicative of mood - I wouldn't get hung up on needing to attain a particular level - but just a dose that makes you feel OK.
Having said that 50mcg patch is not a high dose, although if you are peri and still have quite a strong cycle - then during the oestrogen peaks mid cycle your levels may well be fine. If the aim is for these levels to be high during the whole cycle I doubt whether this would be achieved with a 50 mcg patch. However you may feel well on this dose or even a small increase in patch size?
If you are peri then breakthrough/withdrawal bleeding can sometimes occur randomly due to your own hormonal fluctuations .
Hurdity x