  The R-value is a measure of the strength of photospheric magnetic Polarity
Inversion Lines (PILs) in Active Regions (ARs). This work investigates the
possibility of a relation between R-value variations and the occurrence of
X-class flares in ARs, not in the solar photosphere, as usual, but above it in
regions, closer to where flares occur. The modus operandi is to extrapolate the
Solar Dynamic Observatory's (SDO) Helioseismic and Magnetic Imager (HMI)
magnetogram data up to a height of 3.24 Mm above the photosphere and then
compute the R-value based on the extrapolated magnetic field. Recent studies
have shown that certain flare-predictive parameters such as the horizontal
gradient of the vertical magnetic field and magnetic helicity may improve flare
prediction lead times significantly if studied at a specific height range above
the photosphere, called the Optimal Height Range (OHR). Here we define the OHR
as a collection of heights where a sudden but sustained increase in R-value is
found. For the eight case studies discussed in this paper, our results indicate
that it is possible for OHRs to exist in the low solar atmosphere (between 0.36
- 3.24 Mm), where R-value spikes occur 48-68 hrs before the first X-class flare
of an emerging AR. The temporal evolution of R-value before the first X-class
flare for an emerging AR is also found to be distinct from that of non-flaring
ARs. For X-class flares associated with non-emerging ARs, an OHR could not be
found.
