Are concentration checks made at full caster level if you are casting a spell with a lower CL than your highest possible?

Question

In a related question I had asked when you must choose if you are using a lower caster level when casting a spell.

If for some reason you want to cast a spell at a lower CL and are forced to make a concentration check, such as casting defensively, what CL do you use? The one you are casting the spell with or your actual CL?

Caster Level

You can cast a spell at a lower caster level than normal, but the caster level you choose must be high enough for you to cast the spell in question, and all level-dependent features must be based on the same caster level.

I am asking this question in a general sense so that it works for Pathfinder. The specifics of why I am asking are for Spheres of Power (SoP). In it I am playing a caster who has the focus drawback. I have lost my focus and to successfully cast a spell is Concentration (1d20+ability mod+CL) VS DC 20 + 1/2CL. The 1/2 CL is directly tied to the spell being cast, but is concentration? By casting weaker spells I can have useful effects but with easier to manage DC's.

Focused Casting

Your magic requires you to use an item such as a wand, holy symbol, ring, or staff to create magic. Using magic without your focus requires you to make a concentration check (DC 20 + 1/2 the caster level) to produce the desired effect. Failure means time (and any spell points) are spent, but no effect happens. If a focus is lost, stolen, or broken, the caster must create a new focus by securing the necessary item and spending 8 hours bonding with it. At the GM’s discretion, however, another caster’s focus may be used instead.

Lower SoP CL

If a caster chooses to use an effect at a lower caster level than his maximum, the DC is also lowered.

Answer 1

The DC of the check is reduced, but your bonus to concentration is not

The DC of the concentration check is based on the caster level of the effect you are producing. Note:

Using magic without your focus requires you to make a concentration check (DC 20 + 1/2 the caster level)

The caster level invoked is not your caster level, it is the caster level (of the magical effect).

The rules for handling concentration checks in the Spheres system helpfully describe a bit further:

When a Sphere caster makes a concentration check, instead of rolling a d20 and adding his caster level + his casting ability modifier, he rolls a d20 and adds his MSB + his casting ability modifier to the roll. Treat an effect’s caster level/2 as the effective spell level for this purpose. A spellcaster may always choose to manifest a magical effect at a lower caster level than his total in order to make a concentration check easier.

Your Magical Skill Bonus, and thus your bonus to concentration checks, is independent of the CL of the effect you are producing, so you get your full bonus to the check regardless of the CL of the effect. Though this section specifically addresses concentration checks made for the normal reasons in Pathfinder's main rules which cause concentration checks, and therefore describes how to convert the CL of the effect to a spell level for use with those rules, it also makes clear the intention: you can deliberately reduce the CL of the effect to make concentration checks easier.