Bryndraenog is only two fields away from England, although as Mr Payne pointed out the Teme hereabouts is no real border, either geographically or historically.
Around the time Bryndraenog was built - the timbers were felled in 1436 - the bard Ieuan ap Hywel Swrdwal came to sing a praise poem to the new building and it's owner Llywelyn Fychan. Llywelyn Fychan did not trace his ancestry to the main descent group in Maelienydd, that of Elystan Glodrydd, but rather to one Hywel Athro. Perhaps Llywelyn was rhingyll or reeve to the local estates of Richard of York who had inherited the Mortimer lands in 1425 - Bryndraenog is at the entrance of a small valley called Cwmyrhingyll. This is all discussed in the RCAHM volume Houses & History in the March of Wales Radnorshire 1400-1800, a book that really should be in every Radnorian's library. The volume also includes a partial translation of Ieuan ap Hywel Swrdwal's poem, but as there seems to be no translation of the entire poem readily available here's my rough translation:
The night the generous Son of Grace was born a star appeared as a sign to drag a thousand from the fiery pit and the blind from their darkness. And a second time after Jesus, the journeying star of Owain: it was brighter than, woe for many, a myriad of smaller stars. There is a star in Maelienydd, a proud maid of lime and wood, daughter of the king of sunshine, this court is the countess of summer. Bright daylight, all praise to her, is seen at night in our land. The duke has many houses, none of them surpass this, many do not know whether this is the moon or daylight?
Llywelyn Fychan, my draught of mead, the son of Ieuan owns it, the stout, generous line of Ieuan of our land, in the eighth degree from the line of Hywel Athro. Great is his praise on the top strings, the line of Meurig, miracle of the bards. There's no praise of the privileged ranks without the topstring of Bugeildy. How pleasant, by St Chad, to come to him through yonder Teme. He'll win words of greeting, a famous man with a pleasant office; he'll know amusement, joking tales, he'll know the refined words of wise men. I'll study when I alight, eyeing the shining white lime and see, between me and home, a looking-glass from heaven's goldsmith. There's patronage here for me, in a vale of windows. Like the city of Rome, a countless number of patterned glass and stone. None who comes could swear, was it a man or an angel who built his house? If it was a man he built well. Joints, trusses, a knot of Tristan, packed crossbeams, a virtuous Christian, the good craftsmanship of the new hall's sanctuary. a chapel amidst great bays, a court like the houses of Cheap, its face covered in lime. A holy framework, by the rood, a young man's ancient fortress; the sun's candle, chieftain of the close, the wise son of Ieuan's Celliwig; heaven's kinswoman, white-smocked, a stone cloister, St David's glebe; allow the lord, a collared hart, the life of Noah in his new hall.