VR Works 360 stitching top/bottom image with middle part of panorama

Hello. We’re working on creating monoscopic panorama with the VR Works 360.
We have set cameras which are arranged horizontally (wideangle cameras which do not cover top and bottom areas) which declared as “euqatorial”. To cover top and bottom we add two fisheye cameras that shoot up and down and declared as “general”.
The stitching of images from wideangle cameras works perfectly and performs good quality middle-area of panoram.
But when we try to apply images from fisheye cameras we get a lot of artifacts on the boundaries between the horizontal image and the image from the top / bottom. We think that the reason of such the result is that VR Works 360 stitches horizontal pieces of panorama but pieces from the top / bottom are simply superimposed on top.
In a nutshell it seems that top/bottom fisheye images just merged with middle panoram,
Could you advise if there are any methods that can exactly stitch top/bottom images with central(middle) part of panorama ?