it's both, better glass doesn't make the image bigger, just makes it clearer. combine bigger with clearer, and you have a lot nicer picture to look at. It just costs money to have it all. I've been behind a couple tango 4's, and for the money, I like them. If you hate your's your going to want to step up to really good glass. The tango 4 looks a bit like the nsx to me, not awesome, but certainly good and usable. I keep my magnification low until I need more, so field of view on max isn't really something I put too much stock into. If you like to be on max power all the time, it probably matters more to you. Some guys struggle with target acquisition, and some can just throw their rifle up and see what they're looking for. It all comes down to what matters to you, you can read for days, but you have to get behind them to know what you like, and to know what matters to you.
As far as understanding goes, it's pretty simple. It's how much area you can see at any given distance. 3.7 @ 100 or 4.4 @ 100, or whatever it is at any given power. Fov, shrinks as magnification goes up for the most part, Some scopes will tunnel at lower power where they don't offer any more fov as the power goes down below a certain point, ( defeating the purpose, but looks good on paper) so obviously, the fov doesn't go up until you get past that point on that scope, so on and so forth.
Lots of good options.
Just keep in mind when your dealing with high zoom ration scopes in ffp, you'll have to deal with your reticle going into borderline useless zone on it's lower magnifications. I think the 525i is about right on in this department . 8x zoom ratio scopes in ffp just don't work for me, they take the reticle outside of it's purpose, and defeat the point of low power, quick target acquisition on low power. All opinions here of course. Everyone likes what they like. It's good to research on forums, just know that a lot of the opinions you'll get come from guys that have never looked through a scope, let alone a good one.
I'll probably make a few guys mad, but in my opinion, ffp scopes with over 5x zoom ratios are a waste for the most part. It's just too tough to keep the subtentions useful. Who knows, they'll probably come up with a scope that keeps the subtentions useful across 10x zooms in ffp? Has to go somewhere from here.