Here is the scenario: A party has been giving chase to a spellcaster and corners them in an alley. Initiative is called for, and two archers in the party with higher initiative than the spellcaster decide they are both going to ready their actions of shooting their bows, to be triggered if the spellcaster begins to cast a spell.
On the spellcaster's initiative, the spellcaster attempts to cast Dimension Door(a level 4 spell), triggering the attacks of both archers. Both archers make their To Hit rolls, and the 1st archer does 3 points of damage and the 2nd does 5 points of damage.
My question is about the Concentration Check formula, which states:
If you take damage while trying to cast a spell, you must make a concentration check with a DC equal to 10 + the damage taken + the level of the spell you’re casting.
It is my understanding that the spellcaster needs to make two concentration checks, one for each source.
For the first concentration check, the formula would be: 10 + 3(damage taken) + 4(level of spell) = 17.
*** For the second concentration check, is the damage from the second arrow treated as separate damage or does it accumulate? ***
In other words, should it be: 10 + 5(damage taken) + 4(level of spell) = 19.
or: 10 + 3(damage taken from arrow number one) + 5(damage taken from arrow number two) + 4(level of spell) = 22.
In my opinion, the additional damage should accumulate, meaning the more incoming damage, the more difficult to concentrate on the completion of the spell?
All my efforts to find an answer only talked about different damage types, but nothing on accumulating damage.
If it does NOT accumulate, can you cite something in the rules, or state whether this is opinion?