VAR("") does not work within some expressions

Hi,

My Virtuoso and Spectre Version: ICADVM20.1-64b.NYISR30.2

I have an expression where the EvalType is "sweeps". Here is the expression (I also attached the snapshot):

(peakToPeak(leafValue(swapSweep(delay(?wf1 clip((VT("/clk0") - VT("/clk180")) (VAR("mt_stop") - (4.0 / VAR("datarate"))) VAR("mt_stop")) ?value1 0 ?edge1 "rising" ?nth1 1 ?td1 0 ?tol1 nil ?wf2 clip((VT("/tx_padp") - VT("/tx_padn")) (VAR("mt_stop") - (4.0 / VAR("datarate"))) VAR("mt_stop")) ?value2 0 ?edge2 "rising" ?nth2 1 ?tol2 nil ?td2 nil ?stop nil ?multiple nil) "VDD_FIXED_NOISE") "VREGLN_cmode" 0.85 "VREGDRV_novn" 0.4 "datarate" 1.658e+10) ?overall t) / 10.0)

What this expression does is that it compares the delay between the output data with respect to a reference clock. I then get this information for two conditions (VDD_FIXED_NOISE = 0 or 10mV) to get the effect of the supply-induced jitter. In the expression, I need to give the value of each parameter in different modes to distinguish them from each other. Now I want to sweep the base supply values and see the supply variation effects. For example, I want to change VREGLN_cmode from 0.85 to 0.81 and see how my supply-induced jitter changes. For that, the hard way is to copy the expression and change that value accordingly (e.g. "VREGLN_cmode" 0.81). I'm looking for an easier way to use a variable in the expression. Something like VAR("VREGLN_Sweep"). But I see it doesn't work in my expression and it gives an eVal error. I tested this before in other expressions (not sweep type) and it always worked. I have only one test and these variables are all Design Variables and not Global variables.
I want to know what mistake am I doing here and is there a way to make this work. Sorry that if I could not explain better my inquiry. Thank you.