I am attempting to look at how a behavioural covariate is related to differences in brain activation.
I have a number of glt terms that look at how my quantitative covariate relates to various various conditions and/or contrasts.

But in the output, the maps that include the covariate are, in many cases, identical (both the coefficient maps and the t maps)
My design has two time points, and 2x2 conditions of lexicality (lex) and first/second languages (L1L2).

So the two following glt terms are meant to be looking at how my covariate (a individual measure of sensitivity to word frequency) relates to activation for words in each language

-gltCode L1:wrd:freq 'L1L2 : 1*L1 Lex : 1*wrd freq : ' \
-gltCode L2:wrd:freq 'L1L2 : 1*L2 Lex : 1*wrd freq : ' \

Interestingly, other glts also return identical maps, but ones that are different from the above, so for example the following all return identical maps:

-gltCode L1:prnt:psd:freq 'L1L2 : 1*L1 Lex : 1*psd freq : ' \
-gltCode L2:prnt:psd:freq 'L1L2 : 1*L2 Lex : 1*psd freq : ' \
-gltCode L1:psd:t1:freq 'L1L2 : 1*L1 Lex : 1*psd Time : 1*Time1 freq : ' \
-gltCode L2:psd:t1:freq 'L1L2 : 1*L2 Lex : 1*psd Time : 1*Time1 freq : ' \
-gltCode L1:psd:t3:freq 'L1L2 : 1*L1 Lex : 1*psd Time : 1*Time3 freq : ' \
-gltCode L2:psd:t3:freq 'L1L2 : 1*L2 Lex : 1*psd Time : 1*Time3 freq : ' \

Am I misunderstanding the interpretation of the covariate and what it means in glts such as these?
Thanks