direct3d camera aspect ratio/scaling problem

i'm controlling slimdx/c# direct3d application. i configured camera per textbox way:

private boyant cameraz = 5.0f;
camera = new camera();
camera.fieldofview =(float)(math.pi/2);
camera.nearplane = 0.5f;
camera.farplane = 1000.0f;
camera.location = new vector3(0.0f, 0.0f, cameraz);
camera.target = vector3.zero;
camera.aspectratio = (float)initialwidth / initialheight;

the sketch rotational slight decent matrix.rotationyawpitchroll mesh.drawsubset(0). all else seem normal.

my problem 3d rope (thin retard box), feeling side, mountain vertically, seem thicker it's horizontal. i've attempted change aspectratio 1, it's worse. by hearing error, i found out it's looks many normal aspectratio around 2.6. since wrong?