this isn't really fox specific, but i have a question on shield di.
i know the pros tend to tilt their shield towards their opponent to better prevent shield poke (say vs falco)
but then how do you shield ASDI falco's Dair away if you're tilting the shields towards him? if you can't do both, which would be the better choice?
You can't tilt your shield during shield stun (afaik), so if you wanted to protect yourself from Peach's dsmash, you would probably want to tilt your shield down and towards her, then once you start getting hit, smash the stick away. You'll almost always get the shield SDI vs. multi-hit moves like Peach's dsmash or Fox's dair, but you have to be careful about angling your shield towards the opponent for too long because if you don't change the stick's angle before hitlag ends, you will buffer a shield ASDI input and go towards them.
To answer your question more broadly, I would focus on just using shield DI or shield angling, not both. A lot of shield angling isn't even about protecting yourself, it's about shielding the attack slightly earlier than you normally would. This can put the opponent into hitlag sooner than they expect and cause them to input their FF during hitlag (usually resulting in a missed FF and L-cancel). Even if it doesn't throw them off, the amount of shield stun you will have by the time the opponent reaches the ground may be reduced. This is usually dependent on when they aerial and what angle they come at. If they time their aerial so that it would hit your shield regardless of you angling or not, obviously you won't gain any advantage. If a is Fox doing a FH nair so that the hitbox is out when he is in the space above your head, then you can see how angling your shield up to get hit a couple frames earlier could help you get a shield grab before his shine.
When you are angling to protect yourself, make sure you are actually protecting yourself and not giving up the chance to shield SDI away. I think Fox's shield is pretty good on his front, but his tail can get you shield poked a lot if you're on platforms or facing away from the opponent, and his ears can get poked if your shield shrinks a little. Falco's dair, specifically, is kind of hard to shield poke with. His jump height isn't conducive to shield poking in SHFFLs because he stays pretty low, and the hitbox is too round/jointed to really poke beneath shields. By contrast, you can watch Kage's Ganon get shield pokes all the time because he can do super low stomps so that only the very top of the dair is above the stage. Marth also gets a lot of pokes with dtilt going under shields because it's a very thin hitbox, or he can poke with the long, flat ending hitbox of each of his aerials.
Light shielding can also be a useful alternative to shield angling. It usually ends up acting as a more reliable shield angle+shield DI away combo. The extra shield area prevents pokes while the reduced traction causes you to slide further from the attack (it can often get you out of aerial-shines if they weren't super deep, especially vs. Falco who has almost no range on the front of his shine). The downsides to light shielding are that you take more shield damage (you can easily get your shield broken if you were already at sub-50% shield health) and you spend a longer length of time in shield stun. If you shield SDI an attack away, you can usually counterattack really quickly, but if you light shield you will tend to reset to neutral instead depending on how unsafe their attack on your shield was.
Especially happy about the 2nd game vs Peach on FoD. 
