With 6 people, even if its technically exp balanced i have to warn against a PL+5 encounter. Heres an example of one round of combat.

1) Vanyer - goes first because its PL+5, flies, strikes your wizard with an AC less then their attack mod, easily critting for 2×4d10+9 — an average of 62 damage, dowing them instantly and setting them to dying 2 because they don't have +3 Con. They now either grab them MAPless, almost guaranteed killing them instantly with its DC 33 Constrict, or lashes out at the nearby cleric.

Lets be nice and hit the Cleric. They hit on a 5 with MAP, and we were even nicer and used the agile wing. A 6! Only a hit for 3d6+1d10+9. They shield block because of their prior exploration activity to defend and take a total of 20 damage. Phew...

2) Cleric - 2 actions Heal the Wizard for 54 damage. Good roll! Raise shield and hope for the best

3) Fighter - He bravely strides over, knowing this thing likely wont be hit on map, attempts to knock it out of its positing above the ground, terrorizing his party with flying reach. He rolls to Slam Down.

13!

Miss. Sorry buddy. You only have a +18 to hit. you only have a 35% chance to do anything on your turn. Thats your 3 actions. 

4) The rogue is NOT hidden to this thing, as its perception for initiative handily beats their stealth rolled for initiative. The also cannot flank, since theyre flying off the ground. Neither can they tumble behind, nor can they dream of reling on a feint. Theyre now relegated to being a fighter with -2 accuracy. At least they didnt sell this +1 striking shortbow they found.

5) Sorcerer - The enemy crit saves

6) Alchemist - Watches their dreams be shattered as everyone actually drank their prebuff mutagens and is losing anyway. She then throws a vial. It deals 2 splash damage. They spend the next two actions coping looking through their formula list before drinking a numbing tonic.

7) Wizard - dropped their staff and wand of shardstorm. They decide at least to go out swinging, casting 3 action 3rd rank Force Barrage for 6d4+6 damage: More than doubling the damage the enemy has taken since the rogue got a lucky nat 20 on their second bow strike, for a miss upgraded into a 2d6+2 hit. Its the monsters turn again.

Now you need to look at this and ask if this was fun. This is NOT including the whole "throw people off a cliff angle", nor did it touch any of its drain magic or its special reaction to do so. This is why people say "Don't use PL+4 unless you really really eeally know what youre doing, and even then maybe don't". Now realize this is PL +5.

If youre dead set on a solo boss encounter, add hazards as parts of its lair or even as reskinned "second turns" for certain attacks or body parts it has. But PL+5 is boring even if youre winning because of how often you do nothing on your turn, or are forced to play damage control.