Kinda need to see your decklist tbh. I found a lot more success when I went to eight 2-drops and more spells; the versions that play 10-12 low drops just end up playing into Boros's hand by giving them convenient burn targets. I currently run a playset of Deathdealer and Lion, 5 4-toughness 3-drops (3 Courser, 2 Annie) and of course the set of Rhinos. You want the most resilient cards available to you against these guys, and you want the extra spells (mainly Bile Blight, also Downfall) to get rid of their early beats. If Outpost Siege gets rolling you're in a lot of trouble, but Courser plays a similar role for you, so you have some way to recoup the card advantage Siege gives them.

This matchup gets a lot better post side-board. Get all the Drown in Sorrow and Bile Blight available to you, grab your Back to Nature for blowout potential and maybe consider a Murderous Cut (if you think Stormbreath is lurking) or Glare of Heresy (if Mentor/Soulfire are giving you bigger issues). Don't worry about dissynergy with Back to Nature and Courser of Kruphix. You're only using BtN against two things: Outpost Siege (where you end up giving them a 2-for-1 with Courser/BtN for Siege, but (a) the Courser/Siege trade is a win for you b/c Siege does the card advantage job better, and (b) that lost card advantage pays for itself on your opponent's next upkeep), and Chained to the Rocks (where you're not infrequently trading Courser for Anafenza, Rhino, or even another Courser). I'll grant my sideboard is STACKED against Boros Aggro (perhaps too much given other troublesome matchups), but I run the 4th Bile Blight and a playset of Drown in Sorrow. Finding even one of the Drowns is usually gg if they can't stick an Outpost Siege, because almost everything we have dodges Drown in Sorrow outright (and the one creature that doesn't by default, Rakshasa Deathdealer, can effortlessly pump itself out of lethal range).