1.2 will be fine for your ported 10". You will lose SLQ (Sound Level Quality)ported but gain SLP (Sound Level Pressure), the bass will generally be beefy when porting but the bass wont be as tight if you SEALED your box! In other words: Same Sounding Thud(port) vs Dynamic Boom(seal)! Also when porting a box you need more box area space. Sealed needs less room... ...leaves more room for the golf clubs
If I were you, Id ditch the 10" Ported Box idea and get a 12" Sealed in your 1.2 or 2x10" but you'll need 1.5 for that!
Good Luck
Mark
Pioneer DEH-P8200R CD Deck w/4.2volt pre-out
Pioneer 12xCD changer
2 x 12" JL Audio-W0
350 wattRMS 350 Zapco Competition Series Amp
1.0 farret Stinger Capacitor
Sealed 3.0 cubic/ft BOX
4 gauge insulated wire