OK, I feel like stirring the pot a little ::
I always get a little frustrated when people get so "wrapped around the axle" with nomenclature. I don't think there would ever be a question what some who refers to his/her fortified fruit wine as Port, is trying to say. Just like correcting someone who asks for a "Kleenex" even though the actual brand of facial tissue may be different. We all make wine because we like being able to make our wines "our own". we do this by thinking outside the box. At the end of the day, if someone say's they made a port wine, I think it's pretty clear they fortified some sort of wine with a higher alcohol. That being said.
My port wine was made from a bucket of Brunello juice that stopped fermentation at 1.01 sg. I decided to add the strongest proof everclear I could get (195) because I didn't want to dilute the actual flavor of the wine too much by adding a weaker brandy. If I were to make a port intentionally i would never try to interrupt and fermentation simply because that's more of a crap shoot. I believe you're always best fermenting to dry. Mostly because you never know what life has in store for you. you may not beable to check you fermentation progress regularly and I'm certainly not going to get up in the middle of the night to check fermentation. I prefer to ferment dry and as I mentioned earlier, back sweeten with grape concentrate instead of a simple syrup. This will help with flavor. I had a friend of mine fortify a batch of Barolo with home made Kalua and I have to admit. It was pretty darn good. He calls it a Kalua Port, whether that is technically correct is up for debate but I DO call it good
I've never made a fruit wine so I will not comment on that. There are so many ways to make a port style wine from grape juice (red wine) I would just recommend the following basic rules. after that, have some fun with it.
1)Out of convience, I would ferment, what ever wine you choose, dry, then use the pearson square to fortify to 18 to 20%. (you can raise your SG prior to fermenting but I've never done it that way so I'll let others chime in there)
2) back sweeten with a grape concentrate like WineExperts.
3) use the Peason Square to get the final alcohol content you desire. Keep in mind, the weaker the fortifier, the more you have to ad.
hope this helps