"relatively more difficult" is a correct and usable phrase in written English.
It can be used to compare two things and indicate that one is more challenging than the other. For example, "The last section of the exam was relatively more difficult than the first."
Due to its distal location relative to the ICA and vertebrobasilar system, stenting an MCA lesion is also relatively more difficult and prone to intraprocedural complication.
If only there were an involuntary reaction to an image, or at least a reaction "relatively more difficult to censor".
In sum, the additional forces imposed upon a helicopter by its very concept delayed its development, made it relatively more difficult to control than fixed-wing aircraft, and, in general, impeded its use.
For rodents, escaping from temporarily poor conditions is relatively more difficult, and therefore we predicted that a population of rodent pests in a monoculture with synchronised periods of absence of the field crop, would do less well when compared with a population in a heterogeneous landscape.
Batch tests indicate that little pH depression is needed to release non-apatite inorganic P (including microbial polyphosphate), while a pH of 4 rather than 6 will release more apatite inorganic P, and that organic P is relatively more difficult to release from WAS. Fractionation analysis of P in WAS can aid in design of more efficient methods for P recovery from WAS.
The input image in the third row is relatively more difficult since several persons walk in a crowd.
Stack overflows and heap corruption, originally two of the biggest issues within software development in terms of potential risk and exposure, are being replaced by the relatively newer and more difficult to identify integer bugs.
The mobility of the detached retina is relatively higher and more difficult to be manipulated due to the size and location of the retinal tears.
The great advantage compared to external approach is that endoscopic revision treatment is technically feasible and relatively easy, no more difficult than the primary endoscopic procedure, with no increase of risk.
In contrast, in relatively poorer areas health resources and spending are relatively scarce, making it more difficult for the lower-SES group to access public health resources and services, and further expanding the inequality in access to and availability of public health resources among different SES groups.
Oil is in fact relatively abundant still, just more difficult to reach.
