Limit on the blending factor values?

Here’s the code:

if( !m_bs )
{
    CD3D11_BLEND_DESC blendDesc{ D3D11_DEFAULT };
    D3D11_RENDER_TARGET_BLEND_DESC& rt = blendDesc.RenderTarget[ 0 ];
    rt.BlendEnable = TRUE;
    rt.SrcBlend = D3D11_BLEND_BLEND_FACTOR;
    rt.BlendOp = D3D11_BLEND_OP_ADD;
    rt.DestBlend = D3D11_BLEND_ZERO;
    rt.RenderTargetWriteMask = D3D11_COLOR_WRITE_ENABLE_RED | D3D11_COLOR_WRITE_ENABLE_GREEN | D3D11_COLOR_WRITE_ENABLE_BLUE;
    CHECK( device->CreateBlendState( &blendDesc, &m_bs ) );
}

float f;
switch( mode )
{
case 0: // 2x brighter
    f = 2;
    break;
case 1: // 50% darker
    f = 0.5f;
    break;
default:
    return S_FALSE;
}

const float BlendFactor[ 4 ] = { f, f, f, f };
context->OMSetBlendState( m_bs, BlendFactor, 0xffffffff );

50% darker works OK, 2x brighter doesn’t change anything. Why? Is there undocumented limit on the blend factor values?

My render target is DXGI_FORMAT_R10G10B10A2_UNORM, using D3D 11 feature level 11.0.