That is a decent level but some individuals do need higher to feel their best.
Whether you are absorbing the patch efficiently or whether this is mostly your own estradiol depends where you are in relation to menopause.
If you are still in perimenopause the patch could be doing naff all and that's simply your own production, but if you are well into postmenopause, it will almost all be from the patch.
From what I have read, typical levels on a 100mcg patch are often below 300pmol/L, assuming no endogenous estradiol production however there is wide individual variation in this.
You could try increasing in 25mcg increments (ie an extra quarter of a patch) ensuring you have sufficient progestogen to protect the uterus.