I thought I'd post this to help many others out there in the community that have had issues with their Galaxy Watch 4 and tattoos.
I have tried a multitude of things, including using the 25mm epoxy dots. This helped somewhat, but stopped the ECG and body composition working. So I trialled a few things, like cutting the epoxy dot smaller and trying to get the watch to remain on to receive all notifications but also allow the heart rate, ECG and body composition to work. I found by covering the rear centre sensor you still needed direct contact to skin for all other notifications - hence why the 25mm epoxy dots didn't work for the body composition.
I purchased 10mm x 1.5mm clear silicone bumpers, what they use in carpentry for stopping cupboard doors slamming shut. By placing one 10mm bumper in the centre of the sensor on the back, all notifications worked, and the HR, BC, ECG all worked including NFC. The watch also charges with these in place.
Hope this helps people who like myself may be tattooed or scarred. And for reference, I am heavily tattooed shoulder to wrist in solid black and burgundy ink, heavily scarred and my watch now works without issue.
They are ever so slightly dome shape and nestle into the skin softly. Look for "Self-Adhesive Silicone Feet Bumpers Stops Door Cupboard Drawer Cabinet" on eBay. Only a dollar or two for a pack.