Fentanyl is not a very euphoric high. It's nothing compared to oxy. It's a very sedating, nodding kind of drug.
I had the matrix matrix patches, thin plastic sheet, 50s, and I was at about 80-100mg of oxycodone and would get a nod from cutting a quarter of the patch and holding it between my cheek and gums. It doesn't last all that long, 3-4 hours maybe, and it's very strong. When I increased to 1/3rd of a patch I went from a slight nod to total blackout for a couple of hours.
Harm Reduction: Fentanyl hits hard, and by the time you realize you've taken too much it's too late. If you are determined to abuse the patches, I highly recommend you have a sitter watching over you, at least for the first time until you are sure of your dose and tolerance.
Edit: I am assuming you mean micrograms and not milligrams. There are no 25mg fentanyl patches. The strongest patches (100 micrograms) contain 7.5mg total of drug.
Edit 2: I see you mentioned you are using the gel filled patches. I don't have personal experience with them but as I understand it you can still hold the gel in your mouth to good effect (well as good as it gets with fentanyl).