Attackers can target either you or your mount. An area effect affects both of you as long as you're both in the area. You're in an attacker's
reach or range if any square of your mount is within reach or range. Because your mount is larger than you and you share its space, you have
lesser cover against attacks targeting you when you're mounted if the mount would be in the way (as determined by the GM).
Because you can't move your body as freely while you're riding a mount, you take a –2 circumstance penalty to Reflex saves while mounted. Additionally, the only move action you can use is the
Mount action to dismount.