Better reception through an attic vent or through the roof?

[mkintac]

(I searched the forum but couldn't find this specifically addressed.)
I have a question about the best direction to orient an AntennaCraft C290 antenna in my attic. (I don't want to put it on my roof- not yet, anyway.) I live 15 miles north of WashDC and 25 miles W-SW of Baltimore. From antennaweb.org the map shows major signals from DC: 15 miles at 185 deg; and from Baltimore: 25 miles at 62 deg. The TVfool.com report is here. The house is wood frame with vinyl siding. The roof is a typical low-pitch, open gable roof, plywood w asphalt shingles. The ridge runs almost east/west (95deg/275deg), so the flat roof sections face almost north/south (5deg/185deg). At the eastern end of my attic (on the east-facing gable and centered under the ridge) is a small, rectangular, louvered plastic vent, about 15"W x 25"T, with a metal screen over it, but otherwise open. My question is- how should I orient my antenna for best reception of the WashDC signals from the south? Will signals from DC be stronger coming through the small, east-facing vent or coming directly through the south-facing, pitched, plywood, asphalt-shingled roof? I'm sure pointing the antenna toward the vent will let it receive the Baltimore signals better, just not sure about the best orientation to get the DC signals. All thoughts appreciated.

[timgr]

Metal screen is opaque to TV signal.

The best approach is to move the antenna around in the space you have for it, and find the best location. Signal in the attic will be attenuated compared to clear air, and could be distorted locally by wires, plumbing, structure, chimneys, vents, etc etc etc.

[Jake V]

For the Washington, DC signals aim your antenna just a bit west of south (194 degrees on a compass). Scan. Make a record of what you get and the signal levels. Then adjust the antenna a tiny bit at a time.

As timgr notes, find your best view looking south through the roof or end of the house. Note that things like snow on the roof or even rain can cause loss of signals. At best inside an attic you will get about half the signal level shown in the chart.