ISBLANK() not working with "R1C1" reference

that only works if i change reference style in the preferences but that screws up my ability to make calls like this

=SELECT("R"&rowcount&"C1")

where rowcount is a variable named in a FOR/NEXT loop/ can't even remember where i was first introduced to this syntax but i've always written in A1 reference mode using quoted references when i want to make R1C1 calls. So this call selects the cell i have in mind which is the empty first cell in the row i intend to interrogate. i just use the selection with a WAIT command in the macro so i can follow along and debug FOR/NEXT problems. So the quoted reference works fine for the SELECT command. But that very same syntax won't work with ISBLANK. e.g.:

=ISBLANK("R"&rowcount&"C3")

it doesn't work regardless of which style reference i have selected in preferences. and the quoted selection code above works fine even when operating with A1 reference selected (which is to say R1C1 is not checked).

I am still mystified about the background automatic naming that makes something like that selection function work (I would call it variable definition) but whatever happens during the running of the macro does not appear to outlast the macro because when i go to define names after i've run it there is no rowcount, but obviously there is one during the running of macro as it doesn't throw errors and selects the correct cell using that concatentation with the variable rowcount. (like other names, it is quoted when first called out, but after that you don't use quotes).

I came up with a workaround for my conditional test, since i can't get that R1C1 concatenated reference to work with the ISBLANK command I simply select the cell i want to query and then use ACTIVE.CELL() as the reference for ISBLANK and then I use an OFFSET function to write the result of the function into blank space.

MIDDLE_OOBLECK
=FOR("rowcount",5,11,1)
=SELECT("R"&rowcount&"C3")
=IF(ISBLANK(ACTIVE.CELL()),FORMULA.FILL(ISBLANK(ACTIVE.CELL()),OFFSET(ACTIVE.CELL(),0,-2)),FORMULA.FILL(ISBLANK(ACTIVE.CELL()),OFFSET(ACTIVE.CELL(),0,6)))
=WAIT(NOW()+0.000015)
=NEXT()
=RETUN()

but i would still love to know why that reference works fine for SELECT but not for ISBLANK

thanks,

brian