You're right,
It seems for sawfish the window size the same for hide and non hide mode:
$ xwininfo -id 0x4e00007
xwininfo: Window id: 0x4e00007 "plank"
Absolute upper-left X: 0
Absolute upper-left Y: 0
Relative upper-left X: 0
Relative upper-left Y: 0
Width: 122
Height: 768
Depth: 32
Visual: 0x5d
Visual Class: TrueColor
Border width: 0
Class: InputOutput
Colormap: 0x4e00003 (not installed)
Bit Gravity State: NorthWestGravity
Window Gravity State: StaticGravity
Backing Store State: NotUseful
Save Under State: no
Map State: IsViewable
Override Redirect State: no
Corners: +0+0 -1244+0 -1244-0 +0-0
-geometry 122x768+0+0
The same data for both modes.
One interesting data from xprop:
$ xprop -id 0x4e00007
_NET_WM_STRUT(CARDINAL) = 0, 0, 0, 0
_NET_WM_STRUT_PARTIAL(CARDINAL) = 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
WM_STATE(WM_STATE):
window state: Normal
icon window: 0x0
_NET_WM_DESKTOP(CARDINAL) = 4294967295
_NET_WM_STATE(ATOM) = _NET_WM_STATE_STICKY, _NET_WM_STATE_SKIP_PAGER
WM_HINTS(WM_HINTS):
Client accepts input or input focus: False
Initial state is Normal State.
window id # of group leader: 0x4e00001
XdndAware(ATOM) = BITMAP
_MOTIF_DRAG_RECEIVER_INFO(_MOTIF_DRAG_RECEIVER_INFO) = 0x6c, 0x0, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x10, 0x0, 0x0, 0x0
_MOTIF_WM_HINTS(_MOTIF_WM_HINTS) = 0x2, 0x0, 0x0, 0x0, 0x0
_NET_WM_SYNC_REQUEST_COUNTER(CARDINAL) = 81788937
_NET_WM_WINDOW_TYPE(ATOM) = _NET_WM_WINDOW_TYPE_DOCK
_NET_WM_USER_TIME_WINDOW(WINDOW): window id # 0x4e00008
WM_CLIENT_LEADER(WINDOW): window id # 0x4e00001
_NET_WM_PID(CARDINAL) = 18089
WM_LOCALE_NAME(STRING) = "en_US.UTF-8"
WM_CLIENT_MACHINE(STRING) = "sly-sub"
WM_NORMAL_HINTS(WM_SIZE_HINTS):
program specified location: 0, 0
program specified minimum size: 122 by 768
program specified maximum size: 122 by 768
program specified base size: 0 by 0
window gravity: NorthWest
WM_PROTOCOLS(ATOM): protocols WM_DELETE_WINDOW, WM_TAKE_FOCUS, _NET_WM_PING, _NET_WM_SYNC_REQUEST
WM_CLASS(STRING) = "plank", "Plank"
WM_ICON_NAME(STRING) = "plank"
_NET_WM_ICON_NAME(UTF8_STRING) = "plank"
WM_NAME(STRING) = "plank"
_NET_WM_NAME(UTF8_STRING) = "plank"
program specified location: 0, 0
program specified minimum size: 122 by 768
program specified maximum size: 122 by 768
>>> program specified base size: 0 by 0